Screenless reactor for granular moving bed

ABSTRACT

A screenless reactor design is presented. The reactor includes a series of overlapping vanes where solid catalyst can cascade down the vanes. Gas flows across the catalyst by flowing through the vanes contacting the catalyst and then disengaging from contact with the solid catalyst particles.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Division of copending application Ser. No.11/941,553 filed Nov. 16, 2007, the contents of which are herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to the field of fluid particle contact and to anapparatus for contacting fluids and particles. More specifically, thisinvention relates to a moving bed of particles with a cross-flowingfluid.

A wide variety of processes use radial flow reactors to provide forcontact between a fluid and a solid. The solid usually comprises acatalytic material on which the fluid reacts to form a product. Theprocesses cover a range of processes, including hydrocarbon conversion,gas treatment, and adsorption for separation.

Radial flow reactors are constructed such that the reactor has anannular structure and that there are annular distribution and collectiondevices. The devices for distribution and collection incorporate sometype of screened surface. The screened surface is for holding catalystbeds in place and for aiding in the distribution of pressure over thesurface of the reactor to facilitate radial flow through the reactorbed. The screen can be a mesh, either wire or other material, or apunched plate. For a moving bed, the screen or mesh provides a barrierto prevent the loss of solid catalyst particles while allowing fluid toflow through the bed. Solid catalyst particles are added at the top, andflow through the apparatus and removed at the bottom, while passingthrough a screened-in enclosure that permits the flow of fluid over thecatalyst. The screen is preferably constructed of a non-reactivematerial, but in reality the screen often undergoes some reactionthrough corrosion, and over time problems arise from the corroded screenor mesh.

The screens or meshes used to hold the catalyst particles within a bedare sized to have apertures sufficiently small that the particles cannotpass through. A significant problem is the corrosion of meshes orscreens used to hold catalyst beds in place, or for the distribution ofreactants through a reactor bed. Corrosion can plug apertures to ascreen or mesh, creating dead volumes where fluid does not flow.Corrosion can also create larger apertures where the catalyst particlescan then flow out of the catalyst bed with the fluid and be lost to theprocess increasing costs. This produces unacceptable losses of catalyst,and increases costs because of the need to add additional makeupcatalyst.

The design of reactors to overcome these limitations can savesignificantly on downtime for repairs and on the loss of catalyst, whichis a significant portion of the cost of processing hydrocarbons.

SUMMARY OF THE INVENTION

A solution to the problem of corrosion and screen plugging in a movingbed reactor can be accomplished with a new reactor design. The reactorallows for catalyst to flow through a reactor over a plurality of vanes,while allowing gas to flow across the catalyst when the gas flowscounter current to the catalyst. The reactor comprises a plurality ofoverlapping vanes positioned within the reactor. The vanes have sideedges affixed to supports, such as the reactor wall, or a center supportfor a cylindrically shaped reactor. The vanes further have a leadingedge and a trailing edge, where the leading and trailing edges arerelative to the direction of flow of catalyst. Each vane has a trailingedge that overlaps the vane below it, and has a leading edge that isoverlapped by the vane above it. The reactor further includes a catalystinlet at the top of the reactor, a catalyst outlet at the bottom of thereactor, a gas inlet at the bottom of the reactor, and a gas outlet atthe top of the reactor. The vanes are oriented at an angle between 0 and60 degrees from horizontal with the leading edge above the trailingedge. The spacing of the vanes allows free flow of gas between thevanes, while the overlap of the vanes prevents the catalyst from freelyflowing between the vanes with the catalyst cascading from one vane tothe next vane below it.

Other objects, advantages and applications of the present invention willbecome apparent to those skilled in the art from the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a reactor that has a rectangularconstruction;

FIG. 2 is a cross section of a reactor with a rectangular constructionwith angled vanes;

FIG. 3 is a top view of a cylindrically shaped reactor; and

FIG. 4 is a cross section view of a cylindrically shaped reactor.

DETAILED DESCRIPTION OF THE INVENTION

There are many processes that involve the contacting of a fluid with asolid. Moving bed reactors are one such apparatus used in some of theseprocesses. The moving bed reactors comprise a containment device withscreens for allowing fluid to flow across. The screens are designed tohave sufficiently small openings, or slots, to prevent the flow ofsolids through the screens as the solids move through the reactors. Asmany of the processes develop and improve, and the operating conditionsbecome more severe to increase yields, the openings are subject toplugging from coke and/or the deposit of corrosion products. This isespecially true in the hydrocarbon processing industry where sulfurcompounds are reacted and removed from hydrocarbon streams. This limitsthe life of some of the reactor internals and increases downtime for thereplacement of screens. The development of a reactor design that doesnot use screens improves the performance.

The present invention comprises a moving bed reactor that has noscreens. The reactor comprises a plurality of overlapping vanes disposedwithin a reactor housing. The invention allows for the catalyst tocascade down a series of vanes while the fluid percolates upward andthrough the cascading catalyst. In one embodiment, as shown in FIG. 1,the apparatus comprises a housing 10 having a substantially rectilinearshape and that has a front wall, a back wall, and two side walls. Theapparatus includes a plurality of vanes 14 disposed within the housingwhere each vane has a first side edge affixed to a side wall, and asecond side edge affixed to the opposing side wall. Each vane 14 has aleading edge 16 and a trailing edge 18. The leading edge 16 and trailingedge 18 are with respect to the stream-wise flow of solids through thereactor, where the solid will flow across the vane 14 and over thetrailing edge 18. The leading edge 16 of the uppermost vane 14 can beaffixed to the back wall of the reactor, and the trailing edge 18 ofeach vane overlaps in a horizontal position the leading edge 16 of thevane 14 that is nearest and below it. This continues for each vane 14until the last vane 14 in the reactor. The last vane 14 is not above anyother vane 14 and the trailing edge 18 of the last vane 14 directs solidinto a solid collection zone. While it is envisioned that the vanes 14have a substantially planar structure, it is also contemplated that thevanes 14 can be curved or have any geometric configuration thatmaintains the basis of a series of overlapping structures.

The housing 10 includes an inlet opening 20 at the top for theadmittance of solid particles and an outlet opening 22 at the bottom forthe withdrawal of solid particles. The reactor is a fluid solidcontacting reactor, and therefore the reactor includes a fluid inletopening 24 at the bottom of the housing 10 and a fluid outlet opening 26at the top of the housing 10.

In one embodiment, the reactor can include a shroud 28 over the fluidinlet 24, and the bottom 30 of the reactor will be sloped to direct anysolids to the solids outlet opening 22. Although it is not envisionedthat many solids will flow between the vanes 14, the shroud 28 providesprotection against solids entering the fluid inlet 24, and provides ameans to redirect solids that pass through the vanes during anoperational upset.

Typically, this reactor is for corrosive systems wherein the reactantsand/or products are corrosive to the screens that hold the solidcatalyst particles flowing through the reactor. The reactions can plugscreens thereby causing flow maldistributions and dead zones, and inaddition, corrosive reactions can destroy parts of the screens thatwould subsequently allow for material to pass through the screens,thereby causing a loss of catalyst. This is expensive and increasesmaintenance and downtime of the reactor to remedy plugging andcorrosion. The present design provides for continuous uniform contactbetween the fluid and the catalyst, and allows for good separation ofthe catalyst from the fluid before the fluid is removed from thereactor.

A feature of this invention is that there is a large gas disengagingspace 32 above the solids, where solid particles separate from the flowof fluid and drop back onto the bed of solids as the particles movethrough the apparatus. The present reactor provides for continuous flowof solids through the reactor and continuous flow of fluid, usually agas, across the solid catalyst particles. The fluid, after contactingthe solid, enters a disengagement zone 32 where the solid particlesseparate from the fluid.

In one embodiment, the vanes 14 further include a baffle 34. The baffleis disposed proximate to the leading edge 16 of the vane such that thebaffle is below the vane 14 directly above it. In a preferred position,the baffle is positioned at the leading edge 16. While the baffle can bedisposed at any angle relative to the plane of the vane 14, it ispreferred that the baffle be disposed at a substantially perpendicularorientation to the plane of the vane 14. The baffle provides a secondarymeans for preventing the flow of catalyst against the flow of fluid inthe space between neighboring vanes 14.

In another embodiment, the apparatus can further include a second set ofvanes (not shown). The second set of vanes can be disposed in a mannersimilar to the first set of vanes as described above, but either abovethe first set, or below the first set. The second set of vanes providesfor additional fluid inputs, or for additional contact time between thefluid and the catalyst.

The vanes 14 are oriented to facilitate the flow of solids through thereactor, and to control the residence time of the catalyst within thereactor. As shown in FIG. 2, the vanes 14 can be oriented at an angle 40between 0 degrees and 60 degrees relative to horizontal. In a preferredorientation, the vanes 14 are oriented at an angle 40 between 10 degreesand 30 degrees relative to horizontal. The angling of the vanes 14assist in preventing the holdup of catalyst as the catalyst flowsthrough the reactor, and further limits the backflow of catalyst throughthe gaps between the vanes 14.

The catalyst flows down the vanes 14 in a cascade manner. The topsurface of the catalyst, as it flows onto the topmost vane 14 will beclose to the angle of repose for the flowing catalyst. The horizontalspacing of the vanes 14 is preferred such that the trailing edges 18form a line 19 connecting the trailing edges 18. The line 19 ispreferably at an angle relative to the horizontal that is close to theangle of repose for the flowing catalyst. This provides a relativelyuniform bed thickness as the catalyst flows through the reactor.

In another embodiment, the reactor has a cylindrical structure. Thereactor housing 10 is a cylindrical housing 10 with a center support 36,and a plurality of vanes 14 disposed within the housing 10 in a spiralstaircase orientation. The vanes 14 are arrayed such that each vane hasa leading edge 16 and a trailing edge 18, with trailing edge 18 of avane overlapping the leading edge 16 of a vane 14 below it. Across-section view across the longitudinal direction and from above thecylindrically shaped reactor is shown in FIG. 3, where the vanes 14 showthe trailing edge 18 of the vanes, and the leading edges 16 are hiddenby the vanes 14 above them. In a cross-section of the reactor 10 throughthe center support 36 in the longitudinal direction shown in FIG. 4displays the orientation of the vanes 14 relative to one another. Thevanes 14 wind around the center support 36, and have a side edge affixedto the center support 36 with an opposing side edge affixed to theinside wall of the cylindrical housing 10.

The spacing of the vanes 14 is such that there is overlap to prevent thecatalyst flowing through the reactor from passing through the gapbetween neighboring vanes 14. The gap, or spacing, between neighboringvanes 14 is greater than the size of the solid catalyst particles. Thisprovides for a free flow of fluid through the reactor and across theflowing catalyst. The vanes 14 are preferably angled to facilitate theflow of catalyst in one direction across the vanes 14. Also, thehorizontal spacing of the vanes 14 is preferred such that a line formedthrough the trailing edges 18 of the vanes 14 is at an angle close tothe angle of repose for the flowing catalyst.

The cylindrical structure of this embodiment lends itself to a secondplurality of vanes (not shown) disposed within the housing. The secondplurality of vanes is a second spiral of vanes in a similar orientationas the first plurality of vanes, except for a vertical displacement.

With the second plurality of vanes, there are two helixes of vanesformed spiraling around the center support. The vanes in the secondplurality each has a leading edge, a trailing edge, a first side and asecond side. The first side is affixed to the center support and thesecond side is affixed to the cylindrical housing. The vanes are arrayedsuch that the trailing edge of each vane overlaps the leading edge ofthe vane nearest and below it in the second plurality of vanes. Theleading edge and trailing edge are with respect to the flow of catalystthrough the reactor, such that the catalyst flows down onto the vane,along the vane and over the trailing edge of the vane.

The vanes 14 can include a baffle 34 disposed proximate to the leadingedge 16 of the vane 14. The orientation of the vanes 14 is such thatwhen a baffle 34 is affixed to the vanes 14, the baffle 34 is in aposition on the vane 14 to be below the next nearest vane 14 above it.The baffle 34 is preferably affixed in a substantially perpendicularorientation to the vane 14 to which it is affixed.

While the invention has been described with what are presentlyconsidered the preferred embodiments, it is to be understood that theinvention is not limited to the disclosed embodiments, but it isintended to cover various modifications and equivalent arrangementsincluded within the scope of the appended claims.

1. An apparatus for contacting a fluid with a moving bed of solidscomprising: a housing having a first wall and a second wall; a pluralityof vanes wherein each vane has a leading edge, a trailing edge, a firstside and a second side, and where the first side of each vane is affixedto the first wall and the second side of each vane is affixed to thesecond wall, and where the vanes are arrayed at different elevationswithin the housing with the trailing edge of each vane overlapping theleading edge of the nearest neighbor vane below it.
 2. The apparatus ofclaim 1 wherein the housing has a substantially rectilinear shape. 3.The apparatus of claim 1 wherein the housing has an inlet opening at thetop and an outlet opening at the bottom.
 4. The apparatus of claim 1wherein there is a solid inlet opening and a fluid outlet opening at thetop of the housing, and a solid outlet opening and a fluid inlet openingat the bottom of the housing.
 5. The apparatus of claim 1 furthercomprising a second plurality of vanes wherein each vane has a leadingedge, a trailing edge, a first side and a second side, and where thefirst side of each vane is affixed to the first wall and the second sideof each vane is affixed to the second wall, and where the secondplurality of vanes are arrayed at different elevations within thehousing with the trailing edge of each vane of the second plurality ofvanes overlapping the leading edge of the nearest neighbor vane of thesecond plurality of vanes below it.
 6. The apparatus of claim 1 whereineach vane below the uppermost vane includes a baffle disposed proximateto the leading edge of the vane.
 7. The apparatus of claim 6 wherein thebaffle is disposed substantially perpendicularly to the vane.
 8. Theapparatus of claim 4 further comprising a shroud over the fluid inletopening.